Pain is an unpleasant and important stress factor, and a potentially harmful experience for critically ill patients. Pain is harder to evaluate in non-communicative patients, who can´t report their own pain. Behavioral indicators have been proved as useful and reliable for detecting and measuring pain in these patients, and have been the basis for constructing scales for measuring pain, such as the Behavioural Pain Scale (BPS), the Critical Care Observation Tool (CPOT) and the Scale of Behaviors Indicating Pain (ESCID) .